This invention pertains to a control data transmission system for an electronic switching system, and more particularly to a control data transmission system capable of multiple kinds of control signals over a small number of lead lines.
Presently, most wire communication networks comprise an electronic switching systems. An exchange machine of such an electronic switching system comprises a block called a communication path or channel system (SP system) for handling a body of information such as communication data and a block called a control system (CP system) for handling control data for controlling the channel system. An electronic switching system functions by exchanging control data between these two systems.
FIG. 1 is a conceptual view for explaining a conventional control data transmission system in which a CP system controls an SP system.
In FIG. 1, m lead lines for control data and n lead lines for control data validity specification signals connect CP system 1 with an SP system 2.
Here, an example is considered, in which a unit of control data comprising 32 bits is transmitted in two separate blocks of 16 bits, i.e. m=16, and n=2.
FIG. 2 is a timing chart for explaining the control actions of the transmission system.
FIG. 3 is a simplified block diagram of a circuit in the SP system 2 for receiving control data.
In this example, when control data are not valid, a control data validity specification signal is at an "H" level; and when control data are valid, the control data validity specification signal is at an "L" level.
A register [1] 21 receives the 16 bits in a first half of control data at the fall of a control data validity specification signal (1), and a register [2] 22 receives the 16 bits in a last half of control data at the fall of a control data validity specification signal (2).
When all 32 bits of control data are fully lined up, a control data analyzer 3 for analyzing what the control data request needs to be instructed to start an analysis. In this example, a rise in the control data validity specification signal (2) instructs that the analysis be started.
All 32 bits of control data are not transmitted at once, i.e. m=32 and n=1, in this example, to reduce the number (m+n) of lead lines between the CP system and the SP system.
Incidentally, since an electronic switching system for a conventional narrow band integrated services digital network (N-ISDN) adopts a control data transmission system such as one described earlier, a unit of control data does not comprise more than 32 bits.
However, experience obtained from development indicates that, an electronic switching system for a broadband integrated services digital network (B-ISDN) performs a variety of controls which cannot be handled by only 32 bits. Therefore, a unit of control data can comprise as many as 128 bits.
When a conventional control data transmission system such as the one described earlier exchanges multiple groups of control data, as many as 8 lead lines are required for control data validity specification signals (when a unit of control data has 128 bits). However, 16 lead lines for control data are enough for their own purpose. It is expected that the numbers of bits of control data will further increase with future system enhancement. Therefore, a conventional control data transmission system will need a very large number of lead lines, making the diameters of cables too large and connecting work cumbersome and uneconomical.